Merge branch 'master' of github.com:redpony/cdec

1 files changed, 69 insertions, 0 deletions

diff --git a/klm/util/parallel_read.cc b/klm/util/parallel_read.cc
new file mode 100644
index 00000000..6435eb84
--- /dev/null
+++ b/klm/util/parallel_read.cc
@@ -0,0 +1,69 @@
+#include "util/parallel_read.hh"
+
+#include "util/file.hh"
+
+#ifdef WITH_THREADS
+#include "util/thread_pool.hh"
+
+namespace util {
+namespace {
+
+class Reader {
+  public:
+    explicit Reader(int fd) : fd_(fd) {}
+
+    struct Request {
+      void *to;
+      std::size_t size;
+      uint64_t offset;
+
+      bool operator==(const Request &other) const {
+        return (to == other.to) && (size == other.size) && (offset == other.offset);
+      }
+    };
+
+    void operator()(const Request &request) {
+      util::ErsatzPRead(fd_, request.to, request.size, request.offset);
+    }
+
+  private:
+    int fd_;
+};
+
+} // namespace
+
+void ParallelRead(int fd, void *to, std::size_t amount, uint64_t offset) {
+  Reader::Request poison;
+  poison.to = NULL;
+  poison.size = 0;
+  poison.offset = 0;
+  unsigned threads = boost::thread::hardware_concurrency();
+  if (!threads) threads = 2;
+  ThreadPool<Reader> pool(2 /* don't need much of a queue */, threads, fd, poison);
+  const std::size_t kBatch = 1ULL << 25; // 32 MB
+  Reader::Request request;
+  request.to = to;
+  request.size = kBatch;
+  request.offset = offset;
+  for (; amount > kBatch; amount -= kBatch) {
+    pool.Produce(request);
+    request.to = reinterpret_cast<uint8_t*>(request.to) + kBatch;
+    request.offset += kBatch;
+  }
+  request.size = amount;
+  if (request.size) {
+    pool.Produce(request);
+  }
+}
+
+} // namespace util
+
+#else // WITH_THREADS
+
+namespace util {
+void ParallelRead(int fd, void *to, std::size_t amount, uint64_t offset) {
+ util::ErsatzPRead(fd, to, amount, offset);
+}
+} // namespace util
+
+#endif